The present invention relates to a base station in a mobile communication system using a direct spread CDMA (Code Division Multiple Access) and, more particularly, to a multi-beam receiving apparatus in the base station, which receives a radio signal from a mobile station.
FIG. 7 shows a sector receiving apparatus for receiving a radio signal corresponding to one user in the base station of a CDMA mobile communication system using a conventional sector antenna. Referring to FIG. 7, to receive a radio signal of one sector corresponding to one user, normally, diversity reception using two antennas 5011 and 5012 is performed. Signals received by the antennas 5011 and 5012 are frequency-converted into intermediate frequencies by radio receiving sections 5021 and 5022, respectively, and then, subjected to automatic gain amplification. The amplified reception signals are further detected to the baseband signals of I/Q channels by the radio receiving sections 5021 and 5022 using quadrature detection and then converted into digital signals by an A/D converter. The outputs from the radio receiving sections 5021 and 5022 are sent to a searcher section 500 and finger section 510.
In the searcher section 500, the code correlation values of desired wave signals contained in the reception signals are calculated by correlators 5031 and 5032, and delay profiles are generated by delay profile estimation sections 5041 and 5042 on the basis of the calculation results. A path detection circuit 505 detects the reception timings of the multipath signals from the generated delay profiles (the maximum number of detected paths equals the number of demodulators 511 in the finger section 510) and notifies the finger section 510 of the detected reception timings as a reception timing notification signal E.
The finger section 510 despreads the signals from the radio receiving sections 5021 and 5022 using the reception timing notification signal E and antenna number notification signal F output from the path detection circuit 505. That is, an antenna is selected in accordance with the antenna number notification signal F, and each path is despread at a timing notified by the reception timing notification signal E. The despread signals are synthesized by a maximum ratio synthesizer 512 and sent to a decoding circuit 520.
As the antennas 5011 and 5012, sector antennas shown in FIG. 8 are used. A sector antenna is dedicated to one of a plurality of sectors obtained by dividing the periphery (cell) of 360xc2x0. When a cell is divided into sectors, any interference waves that arrive from mobile stations outside a sector can be removed, and interference with the mobile stations outside the sector can be reduced.
However, when the cell is divided into a plurality of sectors, an arriving wave from a mobile station 602 of a certain user in a single sector becomes an interference wave for the desired wave of another mobile station 601, as shown in FIG. 8. Such an interference wave decreases the radio channel capacity and also degrades the transmission quality.
For this reason, when the number of sectors is increased in order to improve the quality and increase the capacity of such a mobile communication system, the number of times of hand-over between the sectors increases along with the increase in number of sectors. This decreases the radio channel capacity. Additionally, since the increase in the number of sectors directly results in an increase in the number of antennas or receivers, the scale and cost of the system increase.
It is an object of the present invention to provide a multi-beam receiving apparatus which allows a high quality and large capacity in a mobile communication system without decreasing the radio channel capacity or increasing the scale and cost.
In order to achieve the above object, according to the present invention, there is provided a multi-beam receiving apparatus comprising a plurality of antenna elements, a plurality of radio receiving means for receiving radio signals through the antenna elements, respectively, a plurality of correlation means for calculating code correlation values of desired wave signals contained in reception signals output from the radio receiving means, a plurality of first beam formation means for individually forming beams on the basis of all outputs from the correlation means, a plurality of delay profile means for individually generating delay profiles on the basis of outputs from the first beam formation means, detection means for detecting, on the basis of outputs from the delay profile means, a reception timing of a multipath formed from the beams formed by the first beam formation means, a plurality of demodulation means for demodulating all the reception signals output from the radio receiving means at the reception timing detected by the detection means, a plurality of second beam formation means for individually forming beams on the basis of all demodulation outputs from the demodulation means, synthesis means for synthesizing outputs from the second beam formation means after weighting, and beam weight control means for weighting, by a beam weight, each output from the correlation means for each of the first beam formation means and weighting, by a beam weight, each output from the demodulation means for each of the second beam formation means.